HEDS-9730 AVAGO [AVAGO TECHNOLOGIES LIMITED], HEDS-9730 Datasheet - Page 2

• Manufacturer Part Number: HEDS-9730
• Description: Small Optical Encoder Modules 480lpi Digital Output
• Manufacturer: AVAGO [AVAGO TECHNOLOGIES LIMITED]

Theory of Operation
A HEDS-973X is a C-shaped emitter/detector module.
Coupled with a codewheel, it translates rotary motion
into a two-channel digital output; coupled with a
codestrip, it translates linear motion into digital outputs.
As seen in Figure 1, the module contains a single Light
Emitting Diode (LED) as its light source. The light is col-
limated into parallel beam by means of a single lens
located directly over the LED. Opposite the emitter is
the integrated detector circuit. This IC consists of photo-
detectors and a signal processing circuitry necessary to
produce the digital waveforms.
The codewheel/codestrip moves between the emitter
and detector, causing the light beam to be interrupted
by the pattern of spaces and bars on the codewheel/
codestrip. The photodiodes, which detect these interrup-
tions, are arranged in a pattern that corresponds to the
radius and count density of the codewheel/ codestrip.
These photodiodes are also spaced such that a light
period on one pair of detectors corresponds to a dark
period on the adjacent pairs of detectors. The photodiode
outputs are fed through the signal processing circuitry.
Two comparators receive these signal and produce the
final outputs for Channels A and B. Due to this integrated
phasing technique the output of channel A is in quadra-
ture with Channel B (90 degrees out of phase).
Output Waveforms

Figure 2.
Definitions
Note: Refer to Figure 2
Count (N): The number of bar and window pairs or counts
per revolution (CPR) of the codewheel. Or the number of
lines per inch of the codestrip (LPI)
1 shaft Rotation = 360 degrees
1 cycle (c) = 360 electrical degree, equivalent to 1 bar and
window pair.
Pulse Width (P): The number of electrical degrees that an
output is high during one cycle, nominally 180°e or 1/2
a cycle.
Pulse Width Error (DP): The deviation in electrical degrees of
the pulse width from its ideal value of 180°e.
State Width (S): The number of electrical degrees between
a transition in the output of channel A and the neigh-
boring transition in the output of channel B. There are 4
states per cycle, each nominally 90°e.
State Width Error (DS): The deviation in electrical degrees of
each state width from its ideal value of 90°e.
Phase (f): The number of electrical degrees between the
center of the high state on channel A and the center of
the high state on channel B. This value is nominally 90°e
for quadrature output.
Phase Error (Df): The deviation in electrical degrees of the
phase from its ideal value of 90°e.
Direction of Rotation: When the codewheel rotates in the
counter-clockwise direction (as viewed from the encoder
end of the motor), channel A will lead channel B. If the
codewheel rotates in the clockwise direction, channel B
will lead channel A.
Optical Radius (Rop): The distance from the codewheel’s
center of rotation to the optical center (O°C) of the
encoder module.
Angular Misalignment Error (E
the sensor in relation to then tangential direction. This
applies for both rotary and linear motion.
Mounting Position (R
rotation to center of Alignment Tab receiving hole.
= N cycles
M
): Distance from Motor Shaft center of
A
): Angular misalignment of